There are 2 categories of abort scenarios in the beginning of a shuttle flight, a pad abort, and an ascent abort.
PAD ABORT
A pad abort is precisely that, a launch abort that occurs while the shuttle is still firmly bolted down to the pad and SRB ignition hasn’t taken place. In any point of the countdown, an abort may occur, be it because of weather conditions or systems malfunction scrubbing the launch, or because the GLS (during the last 9 minutes of the count up until 31 seconds remaining) detected a fault and paused the countdown (or was commanded by a flight controller to do so), or because the RSLS gave a cutoff to the launch in between T-31 seconds and T-0.001 seconds (not kidding. These computers are precise!). Many missions have been scrubbed in many points in the countdown, particularly when tanking is about to occur, or during the Launch Status Check (go/nogo for launch) during the final 9-minute hold. But only 5 missions have had these aborts, and 4 of those have taken the crown for being the most stressful of all aborts: right between main engine start (T-6.6 seconds) and SRB ignition (T-0). Below is a video of all 5.
In most cases, the Redundant Set Launch Sequencer program on the shuttle’s onboard GPCs, gave the cutoff because one or two of the three main engines did not ignite. In other cases, it might have detected a leak within the engines, or a fault on a critical system. When the RSLS gives the cutoff, it is known as an RSLS abort. This abort is most stressful when the engines actually fired, be it one or 2 or all three and then it gets cut off. The shuttle starts to sway with the sudden thrust, and keeps swaying for a couple of minutes until all motion stops. The astronauts onboard know it is only 8 explosive bolts holding down all 4,400,000 pounds of the shuttle in its upright position via its SRBs. It is not a pretty scenario for them when suddenly the shuttle sways forward and back for a few minutes, straining against those bolts. Luckily, no one was hurt in these 5 aborts. Well, the first 4. The fifth never even got to fire the engines (cutoff was at T-7.5 seconds), so no swaying occurred. These missions were attempted later, and succeeded.
ASCENT ABORTS
From T-0 to MECO, there are different abort scenarios that can occur depending on the kind of failure and the altitude/speed/position of the shuttle. In this category, there are 2 subcategories, intact aborts and contingency aborts. In order to select an abort, when called to do so, the commander selects the abort mode in a rotary switch and presses the ABORT button to execute the selected abort. The shuttle then does a pre-programmed set of commands that will put it in the right path and configuration to that specific abort (accelerating remaining engines to max, dumping unnecessary fuel, reorienting the shuttle, releasing the external tank, etc.). This usually happens when an engine, or 2, or all 3 are lost, or a critical system malfunction occurs (life support, APUs, Fuel Cells, etc) during ascent. I will name them from most desirable to least desirable.
ATO: Abort To Orbit. This mode isn’t a real abort, as it actually makes the shuttle reach a lower than planned, but safe orbit, thus requiring just an OMS burn or 2 to raise the orbit to the right one so the mission can start. The moment when this abort becomes available is when CapCom says “Press to ATO”. (no, not the company that makes Street Fighter or Mega Man. This is the CAPsule COMmunicator, the guy whose job is to relay orders and info to the astronauts and receive replies by them. He is the only one who ever talks to the shuttle, and anything that must be told to the astronauts has to go through him. It’s usually an astronaut, because they believe an astronaut would convey info/orders in a way that the crew would understand, being an astronaut himself.)
AOA: Abort Once Around. This abort mode makes the shuttle make one complete orbit before reentering the atmosphere. There’s a short margin in which this abort is possible, right before ATO is possible. However, a (not so critical but meaningful) emergency might cause them to execute this abort anyways. This abort is available also after MECO (Main Engine Cut Off) when needed. It can land on Kennedy Space Center, Florida, Edwards Air Force Base, California or White Sands Missile Range, New Mexico (not preferred since the sand can damage the orbiter, as seen on STS-3, however, the facility’s been upgraded to permit a landing with the least amount of complications should the need for it arise.). Theoretically it can land on any runway, considering it’s long and wide enough, should the emergency arise. This applies to all intact abort modes, except RTLS.
TAL: Trans-Atlantic Abort. This abort mode is selected when ATO is unreachable, and RTLS is either not needed or already unavailable (“Negative Return”). The shuttle has a ballistic trajectory that has it crossing the Atlantic Ocean for a landing in Europe/Africa friendly bases.The ones being selected for TAL sites right now are Moron and Zaragoza Air Force Bases in Spain and Istres Air Force Base in France.
RTLS: Return To Launch Site. This is the fastest, and most dangerous intact abort mode. If an engine failure before TAL capability is reached, or an extreme emergency requiring immediate landing occurs (such as cabin leak), RTLS is activated. If the SRBs are still latched onto the shuttle, it waits till the SRBs are detached and clear, then it executes the abort. If the SRBs are already clear, it immediately executes it. It pitches the shuttle around to aim back at Kennedy Space Center and burns the remaining engines, OMS engines, and RCS thrusters into the flight path until downrange speed is killed. It then accelerates back to Kennedy, releases the tank so it still falls into the ocean, and glides back to Kennedy Space Center as if it were a normal descent and landing. The danger comes with the pitch around of the shuttle while still burning its main engines, resulting in a lot of gravitational stress to the crew AND orbiter, not to mention aerodynamic forces still present at those altitudes, although NASA says it’s already at a sufficient altitude for those aerodynamic stresses to be a non-issue.
The aforementioned aborts are the “intact” abort scenarios, where both orbiter and crew are safely recovered, well, intact. However, if a catastrophic malfunction occurs (all-engine malfunction, multiple APU/fuel cell malfunction, etc), which leaves the orbiter incapable of reaching a suitable landing site, a contingency abort is made. It simply consists of attempting to put the shuttle into a stable glide, aiming at open ocean, until it reaches the survivable altitude and speed limit. There, the crew pops the side hatch, slide a pole out, and bails out of the orbiter, the pole clearing them from the shuttle (they have parachutes latched onto their orange launch and entry suits. Their suits are called the Advanced Crew Escape Suit). There, they parachute down to the ocean. Their backpack also contains survival gear, including a personal life raft. There they wait until search and recovery forces pull them out of the water. As for the orbiter, it is ditched into the ocean.
The same thing can happen if this failure occurs during/after entry interface. Of course, the same survivable speed and altitude limit criteria must be met before bailout is possible, unlike STS-107 Columbia’s case, where the speed and altitude were too great for bailout to be survivable (and, consequently, had their unfortunate deaths for granted, as they could only sit and wait until the crew module broke up) when the orbiter breakup began. Popping that hatch open would have instantly killed the astronauts because of the plasma generated by the high speed reentry into the atmosphere, EVEN with their suits on and sealed. In fact, they found melted pieces of the suits. PIECES. And the body parts supposed to be inside the pieces miles away from said suit pieces, and in several degrees of heat/dismembering damage (a woman heard a noise on that day and went out to find her dog chewing happily on a charred body part. This is no joke. Look it up.) A suit designed to keep your body at a stable temperature even under severe temperatures, MELTED. And they were still being protected by a significant portion of the crew cabin as it broke up. Think about how bad the day was for the person INSIDE the suit when the heat went through the suit. Even worse when the crew cabin broke up and what was left was exposed to the limb-severing, flesh-ripping airstream of 12,500 MPH. And its associated flash-burning due to the friction. IF somehow the suit would have held together, it still didn’t solve the fact that they were still flying at over 200,000 feet, and because of their immensely reduced weight (230,000 pounds of the orbiter to a measly 200 pound guy), their dropping speed would be at an all-time low, and their oxygen reserve would run out before they reach breathable air. May I remind you that the guys who climbed all 29,029 feet of Mount Everest, Earth’s tallest mountain, needed OXYGEN MASKS/TANKS to stay there. 200,000 feet is like vacuum in comparison. May I also remind you that altitudes in excess of 26,250 feet is called “The Death Zone”, since a person slowly suffocates to death, no matter how used he or she is to low air pressure. The body has its limits on how far it can adapt before it gives up, as stated in this article: http://en.wikipedia.org/wiki/Death_zone, and I quote, “Finally, in the "death zone" at 7,000 to 8,000 m (23,000 to 26,200 ft) and higher, no human body can acclimatize. The body uses up its store of oxygen faster than it can be replenished. An extended stay in the zone without supplementary oxygen will result in deterioration of body functions, loss of consciousness and, ultimately, death.” That’s at 26,250 feet. 200,000 feet is like holding your breath and never breathing again until your brain stops. Or being hanged by the neck. Same result. Death by suffocation. (And somehow, there is still a sufficient airstream to rip you apart at 12,500MPH. Nature is clinically bat-shit insane. But so are we for messin’ with it xD)
So, popping the hatch and bailing out at insane speeds and altitude is a big no-no.
And on that note, for my next blog… …REENTRY. …and landing.
…fricken tiles.
No comments:
Post a Comment